Caster wheels such as are used on factory trucks, baggage trucks and the like are sometimes subjected to very high shock loads during use, particularly when the vehicle is traveling at a high speed. The caster wheel axis is horizontally offset a substantial distance from its swivel axis in order to cause the caster to trail properly and, even when the caster wheel is operating under its rated load and is in proper trailing position on the ground, the caster bracket that swivelly supports the ground engaging wheel will be subjected to very high impact forces if the ground engaging wheel strikes a substantial obstruction or other irregularity in the ground while the vehicle is traveling at relatively high speed. Further, when the vehicle is drawn over an irregular surface, the caster wheel will sometimes move out of engagement with the ground. If the caster turns or swivels about its swivel axis while out of engagement with the ground, the ground engaging wheel will not be in a position to roll properly when it thereafter contacts the ground and the caster will be subjected to high lateral forces until the wheel again swings into proper trailing position. If the vehicle is traveling at a relatively high speed, these forces have sometimes been sufficient to break or otherwise damage the caster wheel.
Shock absorbing type caster apparatus such as shown in the applicant's prior U.S. Pat. No. 3,518,714 are adapted to yield upwardly when the wheel engages an obstruction to allow the wheel to pass over the obstruction. It has also been proposed, as shown in the aforementioned U.S. Pat. No. 3,518,714 to provide a swivel dampening brake to inhibit swivelling of the caster when the ground engaging wheel moves out of engagement with the ground. However, the impact forces exerted on the swivel bracket of the caster when the wheel strikes an obstruction while the vehicle is traveling at a high speed have still been sufficiently high to break or damage such caster.
In order to reduce the stresses opposed on the caster bracket when it strikes an obstruction, it has heretofore been proposed for example as shown in U.S. Pat. No. 2,803,545 to provide an anti-friction bearing assembly between the caster bracket and the mounting base and spaced radially outwardly of the swivel axis a distance approximating the amount of horizontal offset of the ground engaging wheel from the swivel axis. However, such a large diameter anti-friction bearing assemblies are very expensive and, moreover, would require expensive large diameter annular seals to prevent damage due to the entrance of foreign material. It has also been proposed as is shown in U.S. Pat. No. 2,440,047 to use a plurality of rollers mounted on the caster bracket for rotation about axes extending generally radially of the swivel axis at uniform spaced locations therearound to engage the caster mounting base and aid in swivelly supporting the caster. However, trucks using casters are frequently used in areas where they are exposed to dust, dirt and other foreign matter and the operation of the caster disclosed in that patent would be impaired if foreign matter accumulated in an area where the rollers operate.